Conventionally, an ejector has been known as a depressurizing device applied to a vapor compression refrigeration cycle device. The ejector of this type has a nozzle portion that depressurizes refrigerant, draws a gas-phase refrigerant which has flowed out of an evaporator due to a suction action of an ejection refrigerant ejected from the nozzle portion, mixes the ejection refrigerant with the suction refrigerant in a pressure increase part (diffuser portion), thereby being capable of increasing the pressure.
Therefore, in the refrigeration cycle device having the ejector as the depressurizing device (hereinafter referred to as “ejector refrigeration cycle”), a motive power consumption of the compressor can be reduced with the use of the refrigerant pressure increase action in a pressure increase part of the ejector, and a coefficient of performance (COP) of the cycle can be improved more than that of a normal refrigeration cycle device having an expansion valve as the depressurizing device.
Further, Patent Document 1 discloses an ejector having the nozzle portion which depressurizes the refrigerant in two stages as the ejector applied to the ejector refrigeration cycle. In more detail, in the ejector of Patent Document 1, the refrigerant of a high pressure liquid-phase state is depressurized into a gas-liquid two-phase state in a first nozzle, and the refrigerant that has been the gas-liquid two-phase state flows into a second nozzle.
With the above configuration, in the ejector of Patent Document 1, boiling of the refrigerant in the second nozzle is promoted to improve a nozzle efficiency as the overall nozzle portion, and the COP is to be further improved as the overall ejector refrigeration cycle.
Also, in the general ejector, a diffuser portion (pressure increase part) is coaxially arranged on an extension in an axial direction of the nozzle portion. Further, Patent Document 2 discloses that a spread angle of the diffuser portion thus arranged is relatively reduced to enable an improvement in the ejector efficiency.
The nozzle efficiency means energy conversion efficiency when a pressure energy of the refrigerant is converted into a kinetic energy in the nozzle portion. The ejector efficiency means energy conversion efficiency as the overall ejector.